[U-Boot] RPi and iPXE with serial console

[Mark Snelling]

Hi,
I am trying to get iSCSI booting working on the RPi 3+ b board. I have
applied the patches on the rpi patch queue to the v2018.03 release and it
builds and boots to the serial console prompt successfully.
The next step was to build the iPXE snp.efi module, this also seemed to go
with issue following the instructions in README.iscsi and enabling the
following...
#define CONSOLE_CMD

I have the resulting snp.efi loading and running with the bootefi command
and get the following log.

U-Boot 2018.03-dirty (Apr 01 2018 - 19:10:55 +0100)

DRAM:  948 MiB
RPI 3 Model B+ (0xa020d3)
MMC:   mmc at 7e202000: 0, sdhci at 7e300000: 1
Loading Environment from FAT... *** Warning - bad CRC, using default
environment

Failed (-5)
In:    serial
Out:   vidconsole
Err:   vidconsole
Net:   No ethernet found.
starting USB...
USB0:   Core Release: 2.80a
scanning bus 0 for devices... 4 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
Hit any key to stop autoboot:  0
U-Boot> fatload mmc 0:1 $kernel_addr_r snp.efi
160672 bytes read in 12 ms (12.8 MiB/s)
U-Boot> bootefi $kernel_addr_r
## Starting EFI application at 01000000 ...
WARNING: using memory device/image path, this may confuse some payloads!
Scanning disk mmc at 7e202000.blk...
Card did not respond to voltage select!
Scanning disk sdhci at 7e300000.blk...
Disk sdhci at 7e300000.blk not ready
Found 3 disks
WARNING: Invalid device tree, expect boot to fail
iPXE initialising devices...Rx: failed to receive: -5
Rx: failed to receive: -5
...
Rx: failed to receive: -5
ok

iPXE 1.0.0+ (8c17) -- Open Source Network Boot Firmware -- http://ipxe.org
Features: DNS FTP HTTP HTTPS iSCSI NFS TFTP VLAN AoE EFI Menu

Press Ctrl-B for the iPXE command line...

At this point I was trying to get to the iPXE console but it's not
accepting any input.

Am I doing anything wrong here?

Thanks,
Mark